Types of wireless networks include infrastructure-based wireless networks and ad hoc wireless networks.
Ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly, techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of ad hoc network nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multi-hopping”) until the packets reach the destination node. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination. For relaying packets to the next node, each node maintains routing information collected through conversation with its neighboring nodes. The routing information can also be periodically broadcast in the network to reflect the current network topology. Alternatively, to reduce the amount of information transmitted for maintaining accurate routing information, the network nodes may exchange routing information only when it is needed.
Ad hoc networks can generally be categorized into two different system architectures which support different control and/or resource allocation protocols. In distributed ad hoc network architectures, each node shares the entire spectrum with other nodes, and each node acts independently in selection of resources (e.g., frequency, time or code allocations). By contrast, in cluster ad hoc network architectures, a clusterhead node acts as a centralized point of control and manages resource allocation, control, and management functions for a cluster of proximate nodes somewhat like a base station in conventional cellular networks. Among other functions, the clusterhead node can direct control information and data traffic to appropriate nodes in the network. Adjacent clusters share resources, such as, time, frequency, or code allocations. The clusterhead node allocates resources among proximate nodes (associated with the clusterhead node) in its cluster based on service requests from the proximate nodes.
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